The continuing and expanding challenges imposed on agronomic cropping systems by weed populations resistant to various herbicides has led to renewed interest in utilizing multiple modes of herbicide action in weed management programs.

Indeed, articles written about and advertisements for products that contain multiple modes of action populate many farm media publications. But, simply because a herbicide premix or tankmix combination includes herbicides representing more than one mode of action doesn’t necessarily mean that each component in the premix or tankmix will be effective against the target weed species of greatest concern.

There are many instances when multiple modes of action and effective modes of action are not synonymous. For example, two-component premixes of soil-applied herbicides containing a PPO inhibitor and ALS inhibitor do not contain two effective modes of action against ALS-resistant waterhemp. Tankmixtures or premixtures of glyphosate and dicamba do not contain two effective modes of action against glyphosate-resistant waterhemp.

Traits and timelines

Soybean varieties with traits conferring resistance to 2,4-D or dicamba have received USDA approvals for commercialization, but as of this writing neither trait has received approvals in certain export markets. Additionally, dicamba-containing products have not received federal or state labels for in-crop application in commercial soybean fields.

Much interest exists about utilizing these new technologies to manage challenging weed populations, but uncertainty remains if these technologies will be broadly planted in 2016. Those who are planning to rely on these traits and technologies in their 2016 weed management programs are encouraged to develop contingency programs in the event these technologies are not broadly available in 2016.